A bur tube, such as the one found in U.S. Pat. No. 5,040,980 entitled Dental Handpiece with Spring Grip Chuck and Lever Release Mechanism, is used in a dental handpiece in connection with a chuck to mount a dental bur, i.e., a drill bit or cutting tool. Normally, the bur or cutting tool is held within the chuck which is, in turn, held within the bur tube.
The bur tube is a relatively thin, small diameter tubular member having a slightly tapered outer surface. Ball bearing assemblies mount the bur tube within the head of the dental handpiece. A rotor is mounted on the bur tube and rotates the bur tube and consequently the bur or cutting tool in response to an air stream which is fed through the handpiece. Conventional rotational speeds are very high, on the order of 400,000 rpm. The parts of the dental handpiece must be carefully made, selected and assembled to assure both proper "in round" and balance for vibration free or "true" rotation at this speed.
Heretofore, a pair of bill bearing assemblies (bearings) have been pressed directly over the outer surface of the bur tube itself. These bearings rotatably mount the bur tube to an inside surface of the head of the handpiece. If the bearings are too loose, the bur tube will be out of balance and cause excessive vibration and premature wear of the parts. If the bearings are too tight, the bearings tend to distort the bur tube causing an "out-of-round" configuration and interfering with proper rotation at high speeds which can lead to premature failure.
The rotor has also been pressed directly over the outer surface of the bur tube. As with the abovedescribed problems that exist when the bearing assemblies are press fit, certain problems occur when the rotor is press fit over the outer surface of the bur tube. That is, if the rotor is too loose, the rotor will slip relative to the bur tube and fail to rotate the bur tube properly. If the rotor is too tight, the rotor tends to distort the bur tube and interferes with proper rotation at high speeds which can lead to premature failure.
The present invention is intended to avoid the foregoing method of assembly and attendant problems.